Method of cleaning semiconductor surfaces

ABSTRACT

Devices and methods of cleaning are described. The methods, and devices formed by the methods have a number of advantages. Embodiments are shown that include cleaning using a supercritical fluid. Advantages include a combination of both chemical and mechanical removal abilities from the supercritical fluid. Mechanical energy for cleaning is transmitted in a homogenous manner throughout a carrier fluid. The mechanical energy provided in methods shown also can also be used with delicate surface features.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/681,481, filed Oct. 8, 2003, which is incorporated herein byreference.

TECHNICAL FIELD

This invention relates to cleaning methods. Specifically this inventionrelates to a method of cleaning high density semiconductor wafers, chipsand assemblies of chips.

BACKGROUND

The development of high density ULSI circuits with sub-micron dimensionshas lead to the requirement to remove unwanted contaminants from thesurface of the wafers used in the production of structures such as highdensity chips along with the high density multichip assembliesconstructed from these chips. This becomes especially difficult inexamples such as a trench in the trench capacitor; deep contactsnecessitated by stacked capacitors in dynamic random access memories(DRAMS); or the use of the damascene process in the production of coppermetallurgy. High density assemblies e.g. those using flip chip or cubepackaging also present significant cleaning challenges. One example of atype of material to be removed includes the residuals left from a filmin which all or a portion of is to be removed. One example of such afilm is a photo-resist. Another example of a type of material to beremoved includes incidental contaminates.

Depending upon the type of contaminant, it may be attached to thesurface by mechanisms such as chemical bonding, mechanical attachment,or a combination of chemical and mechanical mechanisms. The minimumdimensions of particles to be removed has continued to decrease as theminimum feature size has decreased. This has been aggravated by the factthat the vertical dimensions in the chips have not tended to shrink asfast as the horizontal dimensions thus making relatively deeper holesfor contaminate particles to be lodged in. Further, in chip assemblies,the use of smaller diameter solder balls in C4 connections have reducedthe vertical dimension between the chip and the substrate thus makingthe removal of contaminates from the space more difficult.

What is needed is an improved method for cleaning surfaces andstructures in small dimensions such those produced in semiconductormanufacture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an information handling system according to an embodimentof the invention.

FIG. 2 shows a block diagram of a processing unit according to anembodiment of the invention.

FIG. 3 shows a semiconductor wafer according to an embodiment of theinvention.

FIG. 4A shows a stage in processing a surface according to an embodimentof the invention.

FIG. 4B shows a stage in processing a surface according to an embodimentof the invention.

FIG. 4C shows a stage in processing a surface according to an embodimentof the invention.

FIG. 4D shows a stage in processing a surface according to an embodimentof the invention.

FIG. 5 shows a cleaning system according to an embodiment of theinvention.

FIG. 6 shows a cleaning system according to an embodiment of theinvention.

FIG. 7 shows selected electronic devices formed according to anembodiment of the invention.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown,by way of illustration, specific embodiments in which the invention maybe practiced. In the drawings, like numerals describe substantiallysimilar components throughout the several views. These embodiments aredescribed in sufficient detail to enable those skilled in the art topractice the invention. Other embodiments may be utilized andstructural, logical, and electrical changes may be made withoutdeparting from the scope of the present invention.

The terms wafer and substrate used in the following description includeany structure having an exposed surface with which to form theintegrated circuit (IC) structure of the invention. The term substrateis understood to include semiconductor wafers and first level packaging.The term substrate is also used to refer to semiconductor structuresduring processing, and may include other layers, such assilicon-on-insulator (SOI), etc. that have been fabricated thereupon.Both wafer and substrate include doped and undoped semiconductors,epitaxial semiconductor layers supported by a base semiconductor orinsulator, as well as other semiconductor structures well known to oneskilled in the art. The term conductor is understood to includesemiconductors, and the term insulator or dielectric is defined toinclude any material that is less electrically conductive than thematerials referred to as conductors. The term chip assembly, as used inthis application includes the joining of one or more chips to each otherand or to a chip carrier.

The term “horizontal” as used in this application is defined as a planeparallel to the conventional plane or surface of a wafer or substrate,regardless of the orientation of the wafer or substrate. The term“vertical” refers to a direction perpendicular to the horizontal asdefined above. Prepositions, such as “on”, “side” (as in “sidewall”),“higher”, “lower”, “over” and “under” are defined with respect to theconventional plane or surface being on the top surface of the wafer orsubstrate, regardless of the orientation of the wafer or substrate. Thefollowing detailed description is, therefore, not to be taken in alimiting sense, and the scope of the present invention is defined onlyby the appended claims, along with the full scope of equivalents towhich such claims are entitled.

The disclosed cleaning methods and devices are particularly applicableto the cleaning of any surface with intricate or fragile features.Although a number of types of surfaces are within the scope of theinvention, the cleaning of a semiconductor chip or wafer surface is usedin the following description as an example. Semiconductor chips,assemblies of chips, or semiconductor wafers are included in higherlevel devices or methods of forming devices such as information handlingsystems or personal computers. In one embodiment, the personal computershown in FIGS. 1 and 2 includes chips formed using methods describedbelow.

The personal computer shown in FIGS. 1 and 2 includes a monitor 100,keyboard input 102 and a central processing unit 104. The processor unittypically includes microprocessor chip or chips 106, memory bus circuit108 having a plurality of memory slots 112(a-n), and other peripheralcircuitry 110. Peripheral circuitry 110 permits various peripheraldevices 124 to interface processor-memory bus 120 over input/output(I/O) bus 122.

Microprocessor 106 produces control and address signals to control theexchange of data between memory bus circuit 108 and microprocessor 106and between memory bus circuit 108 and peripheral circuitry 110. Thisexchange of data is accomplished over high speed memory bus 120 and overhigh speed I/O bus 122.

Coupled to memory bus 120 are a plurality of memory slots 112(a-n) whichreceive memory devices. For example, single in-line memory modules(SIMMs) and dual in-line memory modules (DIMMs) may be used in theimplementation of embodiments of the present invention. Those skilled inthe art will recognize that a wide variety of memory devices with memorychips may be coupled to the plurality of memory slots 112(a-n).Acceptable memory devices include, but are not limited to, SDRAMs,SLDRAMs, RDRAMs and other DRAMs and SRAMs, VRAMs and EEPROMs, may beused in the implementation of the present invention. One of ordinaryskill in the art, having the benefit of the present disclosure, willrecognize that chips can be used in chip assemblies i.e. packages whichinclude one or more chips.

FIG. 3 shows a wafer 300 of semiconductor material. Semiconductormaterials include, but are not limited to, silicon, gallium arsenide,silicon-on-insulator structures, etc. The wafer 300 includes a number ofindividual chips 310. The chips 310 may be configured to include severaltypes of integrated circuits on single or multiple chips such as memorycircuits, processor circuits, application specific circuits, etc. In oneembodiment, after processing according to methods described below, thewafer 300 is divided or diced into the respective number of chips 310.The individual chips are then incorporated into higher lever systems ordevices such as illustrated in FIGS. 1 and 2. In one embodiment, methodsof cleaning a semiconductor surface are used to clean a surface of awafer 300. In one embodiment, methods of cleaning a semiconductorsurface are used to clean an individual chip 310 after a dicingoperation. In one embodiment, methods of cleaning a semiconductorsurface are used to clean an assembly of chips.

FIG. 4A shows a portion of a semiconductor 400 including a feature 402.In one embodiment, the semiconductor 400 includes a chip or collectionof chips. In one embodiment, the semiconductor 400 includes a wafer. Inone embodiment, the feature 402 includes a trench. In one embodiment,the feature 402 includes a protruding feature. Other features normallyused in the formation of semiconductor devices are also within thedefinition of the feature 402. For illustration, the feature 402 shownin FIGS. 4A-4D is a trench.

A processing layer 410 is shown covering a surface 404 of thesemiconductor 400. Several types of processing layers 410 are includedwithin the scope of the invention. In one embodiment, the processinglayer 410 includes a photoresist material. In one embodiment, theprocessing layer 410 includes a nitride masking layer. In oneembodiment, the processing layer 410 includes an oxide layer. In oneembodiment, the processing layer 410 includes a metal layer. Othersemiconductor fabrication layers are also within the scope of theinvention. As shown in FIG. 4A, the processing layer 410 is formed bothon the surface 404 of the semiconductor 400 and closely contouring thefeature 402.

In one embodiment, the semiconductor 400 is processed within an enclosedchamber 420. In one embodiment, the chamber 420 is used for multipleprocessing operations. In one embodiment, a number of separate chambers420 are used to complete a semiconductor fabrication process. In oneembodiment, a gas atmosphere 422 within the chamber can be controlled byvarying a number of physical variables. In one embodiment, the variablesinclude thermodynamic variables such as pressure, volume, andtemperature.

FIG. 4B shows the semiconductor 400 after a removal operation. In oneembodiment, the condition of the semiconductor 400 shown in FIG. 4Bcorresponds to a level of cleaning achieved using current cleaningmethods. An unwanted particle 412 is shown remaining within the feature402. In one embodiment the particle 412 is a fraction of materialremaining from incomplete removal of the processing layer 410. In oneembodiment, the particle 412 is a foreign particle that was depositedalong with the processing layer 410. In one embodiment, the particle 412includes a foreign particle from a semiconductor processing operationseparate from deposition or removal of the processing layer 410.

In one embodiment, the removal operation used to create the condition inFIG. 4B includes introducing a solvent solution to the surface 404 ofthe semiconductor 400. In one embodiment, the particle 412 remainsbehind after the removal operation due to incomplete dissolution of theprocessing layer 410 in the solvent solution. In one embodiment, theparticle 412 remains behind due to a particle material that dissolvespoorly or does not dissolve in the solvent solution.

FIG. 4C shows the surface 404 of the semiconductor 400 and the remainingparticle 412 within the feature 402. A carrier fluid 430 is furthershown adjacent to the surface 404 of the semiconductor 400. In oneembodiment, the carrier fluid 430 includes the solvent solution used toremove the processing layer 410. In one embodiment, the carrier fluid430 includes a subsequent cleaning or solvent solution. Carrier fluidsinclude, but are not limited to, de-ionized water, H₂SO₄, and H₂O₂. Inone embodiment, only selected surfaces of the semiconductor 400 areintroduced to the carrier fluid 430. In one embodiment, the entiresemiconductor 400 is immersed within the carrier fluid 430.

In one embodiment, the atmosphere 422 within the chamber 420 is adjustedto alter a state of the atmosphere 422. In one embodiment, theatmosphere 422 is altered during a processing time when the surface 404of the semiconductor 400 and the feature 402 are exposed to the carrierfluid 430. In one embodiment, atmosphere is altered to change theatmosphere to a supercritical state. An atmosphere 422 or environment isdetermined to be in a supercritical state (and is referred to as asupercritical fluid) when it is subjected to a combination of pressureand temperature above its critical point, such that its densityapproaches that of a liquid (i.e., the liquid and gas states areindistinguishable). A wide variety of compounds and elements can beconverted to the supercritical state.

In one embodiment, the supercritical state is achieved by varying atemperature within the chamber 420. In one embodiment, the supercriticalstate is achieved by varying a pressure within the chamber 420. In oneembodiment, the supercritical state is achieved by varying both atemperature and a pressure within the chamber 420. In one embodiment,carbon dioxide is used to form a supercritical fluid. Carbon dioxide hasadvantages such as low cost, and moderate temperature and pressureconditions necessary to form a supercritical state. In a carbon dioxideembodiment, a temperature includes 32° C. and a pressure of 73 Atm.

In addition to a carbon dioxide atmosphere embodiment, other suitableatmospheres 422 include, but are not limited to, nitrous oxide, ethane,ethylene, propane, and xenon. In one embodiment, the supercritical stateincludes a supercritical fluid formed from one of the gases listedabove. In one embodiment the supercritical fluid includes ethyl alcohol,ethyl ether or methyl alcohol.

After formation of the supercritical fluid, the supercritical fluidformed from the atmosphere 422 and the carrier fluid 430 mix together toform a substantially homogenous fluid. Under this condition, thehomogenous fluid substantially surrounds the particle 412 within thefeature 402.

FIG. 4D shows the surface 404 of the semiconductor 400 and the remainingparticle 412 within the feature 402 from FIG. 4C. The atmosphere 422within the chamber 420 is altered a second time to remove conditionswithin the chamber 420 from the supercritical state. FIG. 4D shows anumber of bubbles 424 forming at random locations within the carrierfluid 430. In one embodiment, after the supercritical conditions withinthe chamber 420 are removed, the supercritical fluid component of thehomogenous fluid returns to a gas state, causing the bubbles 424 toform. One example of removing supercritical conditions within thechamber 420 includes reducing a temperature. Another example includesreducing a pressure. Another example includes reducing both atemperature and a pressure.

FIG. 4D shows a bubble forming adjacent to the particle 412. The energyprovided by the expanding gas of the bubble 424 dislodges the particle412, allowing it to be flushed away by the carrier fluid. The energyprovided by the expanding bubble is effective for removal of theparticle 412 because it provides mechanical energy to dislodgemechanical/physical constraints on the particle 412. The energy providedby the expanding bubble is further effective to break any bonding of theparticle 412 to the semiconductor 400 such as Van der Waals bonding, orelectrostatic bonding.

Using a supercritical fluid as described in embodiments above has anumber of advantages. Supercritical fluids are recognized as a goodsolvent for many types of materials. A selected supercritical fluid cantherefore provide both a chemical removal mechanism for some materials,and a mechanical removal mechanism for other non-dissolved particles asdescribed in embodiments above.

Another advantage of methods and devices described above includes ahomogenous delivery of energy to the surface being cleaned. Othermechanical cleaning methods such as sonic bath cleaning can createharmonic “hot spots” at locations on the surface where constructive waveinterference amplifies the mechanical energy. Although sonic bathmethods add additional energy for more effective cleaning, in somecleaning situations, the sonic hot spots can damage sensitive surfacefeatures.

Another advantage of methods and devices described above includes theability to use supercritical fluid techniques with existing cleaningprocesses and cleaning solutions. For example, in a current dry cleaningprocess, de-ionized water is used to rinse a surface of a semiconductorsurface. A supercritical fluid method as described above can be used toform bubbles in the de-ionized water. Likewise, in a wet cleaningexample, a solution such as H₂SO₄ or H₂O₂ is used to clean thesemiconductor surface. A supercritical fluid method as described abovecan be added to this wet cleaning example to form bubbles in the H₂SO₄or H₂O₂ solutions. In processes such as those used for multichipassemblies where fluxes and or organic residues are present,chlorocarbons or chlorofluorocarbons may be used as a carrier fluid.

FIG. 5 shows a cleaning system 500. A portion of a semiconductor 510 isshown including a feature 512. An unwanted particle 514 is shown withinthe feature. A carrier fluid 520, similar to carrier fluids described inembodiments above, is shown in contact with a surface 504 of thesemiconductor 510. Similar to embodiments described above, the surface504 of the semiconductor, the feature 512 and the particle 514 arecontained within a chamber 540. The atmosphere 542 within the chamber540 can be controlled to produce a supercritical state. As described inembodiments above, mechanical energy for cleaning particles such asparticle 514 is provided by altering a supercritical state to producebubbles.

In addition to the use of the supercritical state for mechanical energy,a sonic wave generation system 530 is shown in block diagram form,coupled to the carrier fluid 520. In some embodiments, mechanical energyin addition to that provided by the supercritical fluid is desirable forremoval of unwanted particles. In one embodiment, the sonic wavegeneration system 530 includes ultrasonic energy. In one embodiment, thesonic wave generation system 530 includes megasonic energy. Otherfrequencies of wave generation are also within the scope of theinvention.

FIG. 6 shows a cleaning system 600. A portion of a semiconductor 610 isshown including a feature 612. An unwanted particle 614 is shown withinthe feature. A carrier fluid 620, similar to carrier fluids described inembodiments above, is shown in contact with a surface 604 of thesemiconductor 610. Similar to embodiments described above, the surface604 of the semiconductor, the feature 612 and the particle 614 arecontained within a chamber 640. The atmosphere 642 within the chamber640 can be controlled to produce a supercritical state. As described inembodiments above, mechanical energy for cleaning particles such asparticle 614 is provided by altering a supercritical state to producebubbles.

In addition to the use of the supercritical state for mechanical energy,a brush cleaning system 630 with a number of bristles 632 is shown inblock diagram form, in contact with the surface 604. In someembodiments, the mechanical energy supplied by the brush cleaning system630 is desirable for removal of unwanted particles in addition to theenergy provided by the supercritical fluid as described in embodimentsabove.

FIG. 7 shows examples of devices that are fabricated using semiconductorprocessing techniques. Devices formed using cleaning methods describedbelow include, but are not limited to, trench capacitors and devicecontacts, etc. Devices shown in FIG. 7 are not necessarily drawn toscale. Further, the devices shown in FIG. 7 are shown isolated fromother components, connecting structures, and devices for the purpose ofillustration.

A portion of a chip 700 is shown, including a trench capacitor 710formed in a semiconductor substrate 702. The trench capacitor 710includes an insulator layer 712 and a plate 714 within the insulatorlayer 712. In one embodiment, the substrate functions as a second plateof the trench capacitor 710. An aspect ratio of the trench capacitor 710is shown as the depth 716 divided by the width 718. As shown in FIG. 7,the trench capacitor 710 includes a high aspect ratio design, thatrequires a deep and narrow trench.

Advantages such as the homogenous supply of energy from a supercriticalfluid enables more effective cleaning of high aspect ratio features suchas the trench of a trench capacitor 710. While a brush may not penetrateto depths of features such as the trench of a trench capacitor 710,using embodiments as described above, bubbles will form deep within thetrench to provide mechanical energy for unwanted particle removal.

A transistor 720 is shown located on the semiconductor substrate 702.The transistor includes a first source/drain region 722, a secondsource/drain region 724, and a channel region 726 between the firstsource/drain region 722 and the second source/drain region 724. Adielectric layer 728 is located over the channel region 726, and a gate730 is located over the dielectric layer 728. Although a lateraltransistor configuration is shown as an example, other transistorconfigurations such as a vertical transistor are also within the scopeof the invention. An isolation layer 704 is shown located over andaround the transistor 720. Layers such as the isolation layer 704 areused in some integrated circuits to electrically isolate the transistor720 and to space apart additional layers of devices and interconnectionstructures (not shown).

When additional layers such as the isolation layer 704 are formed over atransistor 720, electrical connections must be made through theisolation layer 704 to operate the transistor 720. A first opening 732is shown over the first source/drain region 722, and a second opening734 is shown over the second source/drain region 724. The thickness 740of the isolation layer 704 and a width 742 of the openings 732, 734determines an aspect ratio of the contact openings. Although a conductorstructure or device is eventually deposited within the first opening 732and the second opening 734, it is frequently necessary to clean theopening 732 and the second opening 734 during fabrication.

Similar to the trench capacitor example described above, advantages suchas the homogenous supply of energy from a supercritical fluid enablesmore effective cleaning of high aspect ratio features such the firstopening 732 and the second opening 734. While a brush, or sonic energymay not penetrate to depths of features such as the first opening 732and the second opening 734, using embodiments as described above,bubbles will form deep within the openings to provide mechanical energyfor unwanted particle removal.

In one application, after the wafer processing is complete, chips arediced and joined into higher level assemblies. Prior to joining it maybe desirable to clean the chips to remove debris from the dicingapparatus. Likewise in one embodiment, after assembly, the narrow spacesbetween chips and or between chips and the substrate are cleaned toremove unwanted residue from the joining/assembly processing.

Although devices such as a trench capacitor 710 and a transistor 720 areshown as examples of devices that benefit from the cleaning methodsdescribed above, the invention is not so limited. Other electronicdevices and features are within the scope of the invention.

CONCLUSION

Devices and methods of cleaning described in embodiments above have anumber of advantages. Advantages of cleaning using a supercritical fluidinclude a combination of both chemical and mechanical removal abilitiesfrom the supercritical fluid. The mechanical energy in embodimentsdescribed above is transmitted in an improved homogenous mannerthroughout a carrier fluid. The mechanical energy in embodimentsdescribed above is also improved in an ability to use with delicatesurface features. Supercritical fluid methods as described inembodiments above are also easily integrated into existing cleaningmethods.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiment shown. This application isintended to cover any adaptations or variations of the presentinvention. It is to be understood that the above description is intendedto be illustrative, and not restrictive. Combinations of the aboveembodiments, and other embodiments will be apparent to those of skill inthe art upon reviewing the above description. The scope of the inventionincludes any other applications in which the above structures andfabrication methods are used. The scope of the invention should bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

1. A method of cleaning a semiconductor surface, comprising: placing thesemiconductor surface in contact with a de-ionized water carrier fluid;forming a supercritical fluid adjacent to the semiconductor surface;changing a thermodynamic condition of the supercritical fluid to causegas bubbles in the carrier fluid; and brushing the semiconductor surfaceconcurrently with the gas bubble formation.
 2. The method of claim 1,wherein forming a supercritical fluid includes forming a carbon dioxidesupercritical fluid.
 3. The method of claim 1, wherein forming asupercritical fluid includes forming a nitrous oxide supercriticalfluid.
 4. The method of claim 1, wherein forming a supercritical fluidincludes forming an ethane supercritical fluid.
 5. The method of claim1, wherein forming a supercritical fluid includes forming an ethylenesupercritical fluid.
 6. The method of claim 1, wherein forming asupercritical fluid includes forming a propane supercritical fluid. 7.The method of claim 1, wherein forming a supercritical fluid includesforming a xenon supercritical fluid.
 8. The method of claim 1, whereinforming a supercritical fluid includes forming a carbon dioxidesupercritical fluid.
 9. The method of claim 1, wherein forming asupercritical fluid includes forming an ethyl alcohol supercriticalfluid.
 10. The method of claim 1, wherein forming a supercritical fluidincludes forming a ethyl ether supercritical fluid.
 11. The method ofclaim 1, wherein forming a supercritical fluid includes forming a methylalcohol supercritical fluid.
 12. A method of cleaning a semiconductorsurface, comprising: placing the semiconductor surface in contact with acarrier fluid; forming a supercritical fluid adjacent to thesemiconductor surface; changing a pressure of the supercritical fluid tocause gas bubbles in the carrier fluid; and brushing the semiconductorsurface concurrently with the gas bubble formation.
 13. The method ofclaim 12, wherein placing the semiconductor surface in contact with acarrier fluid includes placing the semiconductor surface in contact withde-ionized water.
 14. The method of claim 12, wherein placing thesemiconductor surface in contact with a carrier fluid includes immersinga semiconductor in an acid cleaning solution.
 15. The method of claim12, further including providing sonic wave energy to the carrier fluid.16. A method of cleaning a semiconductor surface, comprising: placingthe semiconductor surface in contact with a carrier fluid; forming asupercritical fluid adjacent to the semiconductor surface; changing atemperature of the supercritical fluid to cause gas bubbles in thecarrier fluid; and brushing the semiconductor surface concurrently withthe gas bubble formation.
 17. The method of claim 16, further includingproviding sonic wave energy to the carrier fluid.
 18. A method offorming a memory device, comprising: fabricating a number of memorycells on a semiconductor surface; cleaning the semiconductor surface,including: placing the semiconductor surface in contact with a carrierfluid; forming a supercritical fluid adjacent to the semiconductorsurface; changing a thermodynamic condition of the supercritical fluidto cause gas bubbles in the carrier fluid; and brushing thesemiconductor surface concurrently with the gas bubble formation. 19.The method of claim 18, wherein fabricating a number of memory cellsincludes fabricating a number of flash memory cells.
 20. The method ofclaim 18, wherein changing the thermodynamic condition includes changinga temperature.
 21. The method of claim 18, wherein changing thethermodynamic condition includes changing a pressure.
 22. The method ofclaim 18, wherein changing the thermodynamic condition includes changingboth a pressure and a temperature.
 23. A method of cleaning asemiconductor surface, comprising: placing the semiconductor surface incontact with a carrier fluid; forming a supercritical fluid adjacent tothe semiconductor surface; changing a thermodynamic condition of thesupercritical fluid to cause gas bubbles in the carrier fluid; providingsupplemental mechanical energy at the semiconductor surface in additionto the gas bubbles, including providing sonic wave energy to the carrierfluid; and brushing the semiconductor surface while concurrentlychanging the thermodynamic condition of the supercritical fluid to causegas bubbles.
 24. The method of claim 23, wherein forming a supercriticalfluid includes forming a carbon dioxide supercritical fluid.
 25. Themethod of claim 23, wherein forming a supercritical fluid includesforming a supercritical fluid from a group consisting of nitrous oxide,ethane, ethylene, propane, and xenon.
 26. The method of claim 23,wherein forming a supercritical fluid includes forming a supercriticalfluid from a group consisting of ethyl alcohol, ethyl ether and methylalcohol.
 27. The method of claim 23, wherein placing the semiconductorassembly surfaces in contact with a carrier fluid includes immersing thesemiconductor assembly in a halogenated hydrocarbon fluid.
 28. Themethod of claim 27, wherein immersing the semiconductor assembly in ahalogenated hydrocarbon fluid includes immersing the semiconductorassembly in a chlorocarbon solvent.
 29. The method of claim 27, whereinimmersing the semiconductor assembly in a halogenated hydrocarbon fluidincludes immersing the semiconductor assembly in a chlorofluorocarbonsolvent.